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Socket.IOControl Method (Int32, Byte(), Byte())

Sets low-level operating modes for the Socket using numerical control codes.

Namespace:  System.Net.Sockets
Assembly:  System (in System.dll)

Public Function IOControl ( _
	ioControlCode As Integer, _
	optionInValue As Byte(), _
	optionOutValue As Byte() _
) As Integer


Type: System.Int32
An Int32 value that specifies the control code of the operation to perform.
Type: System.Byte()
A Byte array that contains the input data required by the operation.
Type: System.Byte()
A Byte array that contains the output data returned by the operation.

Return Value

Type: System.Int32
The number of bytes in the optionOutValue parameter.


An error occurred when attempting to access the socket. See the Remarks section for more information.


The Socket has been closed.


An attempt was made to change the blocking mode without using the Blocking property.


A caller in the call stack does not have the required permissions.

The IOControl method provides low-level access to the operating system Socket underlying the current instance of the Socket class. For more information, see the WSAIoctl documentation in the MSDN library.


If you receive a SocketException, use the SocketException.ErrorCode property to obtain the specific error code. After you have obtained this code, refer to the Windows Sockets version 2 API error code documentation in the MSDN library for a detailed description of the error.


This member outputs trace information when you enable network tracing in your application. For more information, see Network Tracing.

The following code example compares the results of FIONREAD and the Available property.

		' FIONREAD is also available as the "Available" property.
	   Public Const FIONREAD As Integer = &H4004667F

	   Private Shared Sub DisplayPendingByteCount(ByVal s As Socket)
			Dim outValue() As Byte = BitConverter.GetBytes(0)

			' Check how many bytes have been received.
			s.IOControl(FIONREAD, Nothing, outValue)

			Dim bytesAvailable As UInteger = BitConverter.ToUInt32(outValue, 0)
			Console.WriteLine("server has {0} bytes pending. Available property says {1}.", bytesAvailable, s.Available)

	   End Sub

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.